Biology Notes Ch 8 PDF

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Biology Notes for Chapter 8 Professor Mummaw...

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CHAPTER 8: AN INTRODUCTION TO METABOLSIM

Metabolism - Sum of all chemical reactions occurring in a cell (Catabolism + Anabolism = Metabolism) Catabolism – breakdown of complex organic molecules into simpler compounds (releases energy; generates ATP) Anabolism – building of complex organic molecules from simpler ones (requires energy; requires ATP) - Enzymes catalyze virtually every reaction in cells Condensation & Hydrolysis Condensation - removal of water (Anabolic) Hydrolysis – addition of water (Catabolic) - Biological reactions are “simple” in the sense that the cell only has to remove a water molecule to link two molecules together or add water to break a molecule Two Types of Energy Potential Energy – capacity for work due to location or structure (ex. chemical energy) Kinetic Energy – motion, random movement (ex. thermal energy) Thermodynamics - study of Energy transformations Energy – capacity to do work Organisms are open systems: taking in energy, converting energy, storing some energy, & releasing some to the environment. 1st Law of Thermodynamics – Energy can be neither created nor destroyed but can be transformed from one form to another Living Systems must obey the Law of Thermodynamics

CHAPTER 8: AN INTRODUCTION TO METABOLSIM - A central property of living organisms is the necessity to transform energy 2nd Law of Thermodynamics – every energy transfer or transformation increases the disorder (entropy) of the universe - All energy conversions generate & release some heat Entropy – measure of disorder or randomness - Every time energy is converted from one form to another entropy increases Free Energy (G) – measure of the amount of energy that is released as a reaction proceeds (also called “Gibbs Free Energy”) Spontaneous Reactions - For a system to be spontaneous, the system must either give up energy (decrease H; total energy), give up order (increase in S; entropy), or both 

The change in free energy must be negative

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The greater the increase in free energy, the greater the maximum amount of work that a spontaneous process can perform

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Nature runs “downhill” A system at equilibrium is at maximum stability

- In a chemical reaction at equilibrium, the rate of forward & backward reactions are equal & there is no change in the concentration of products or reactants (system can do no work) - Chemical reactions can be classified as either exergonic or endergonic based on free energy Exergonic Reaction – proceeds with a net release of free energy (negative; spontaneous) Endergonic Reaction – one that absorbs free energy from its surroundings (positive; nonspontaneous) ATP powers cellular work by coupling exergonic reactions to endergonic reactions

CHAPTER 8: AN INTRODUCTION TO METABOLSIM - A cell does three main kinds of work: 

Mechanical work

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Transport work

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Chemical work

- In most cases, the immediate source of the energy that powers cellular work is ATP ATP Powers Cellular Work - The bonds between phosphate groups can be broken by hydrolysis - ATP is a renewable resource that is continually regenerated by adding a phosphate group to ADP 

The energy to support renewal comes from catabolic reactions in the cell

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In a working muscle cell, the entire pool of ATP is recycled once each minute, over 10 million ATP consumed & regenerated per second per cell

Hydrolysis of ATP – losing a phosphate group; exergonic process Regeneration – requires an investment of energy; endergonic process Enzymes Enzymes are substrate specific Substrate – a reactant that binds to an enzyme - When a substrate(s) binds enzyme, the enzyme catalyzes conversion of substrate to product Active Site – typically a pocket or groove on the surface of the protein (enzyme) into which substrate fits - Specificity of an enzyme is due to the shape of the active site (specific substrate) - As substrate binds, enzyme changes shape leading to a tighter induced fit, bringing chemical groups in position to catalyze reaction

CHAPTER 8: AN INTRODUCTION TO METABOLSIM Enzymes Cont’d - Enzymes speed up metabolic reactions by lowering energy barriers (i.e. catalyst) - Enzyme speed reactions by lowering activation energy, or energy of activation Enzymes do not change delta G - Most metabolic enzymes can catalyze a reaction in both forward & reverse direction - A single enzyme molecule can catalyze thousands or more reactions a second - Enzymes are not permanently altered by a reaction & are reusable (almost always) A cell’s physical & chemical environment affects enzyme activity - 3-D structure of enzymes depend on environmental conditions - Temperature, pH, detergents, & salts - Also, concentration of substrate, presence of cofactors, coenzymes, inhibitors Cofactors & Coenzymes - Many enzymes require a nonprotein helper for catalytic activity: these are called cofactors Cofactor Types: bound tightly & permanently to the enzyme or bound loosely & reversibly to the enzyme - Many cofactors are inorganic (zinc, iron, or copper in ionic form), but those which are organic are referred to as a coenzyme (ex. Vitamins) The chemistry of life is organized into metabolic pathways - Enzymes regulate the movement of molecules through metabolic pathways - Regulation of enzymes can therefore regulate metabolism Allosteric Regulation: allosteric = shape Feedback Inhibition - Common mode of metabolic control

CHAPTER 8: AN INTRODUCTION TO METABOLSIM Feedback Inhibition Cont’d - Metabolic pathway is halted by binding of its end product to an enzyme that acts early in the pathway Enzymes – catalysts that speed up & direct chemical reactions Enzymes are substrate specific: Lipases: Lipids Sucrases: Sucrose Ureases: Urea Proteases: Proteins DNases: DNA Naming of Enzymes - Most are named by adding “ase” to the substrate Dehydrogenase – removes a hydrogen Phosphotase – removes a phosphate Compartmentalization Regulation of enzymes by compartmentalization - The cell is compartmentalized & cellular structures help bring order to metabolic pathways (ex. In eukaryotic cells, the enzymes for cellular respiration reside in specific locations within the mitochondria)...